Research On Deformation Feature Of Q2Saturated Loess Tunnel Wall Rock

In recent years, researches on loess tunnel become the hot spot in the engineering industry. With greater efforts on the exploitation of underground space, more and more projects are involved with Q2loess stratum. Yintao project, a large scale inter-basin diversion work, is the biggest hydraulic engineering in Gansu province whose engineering geological conditions are very complicated, including large deformation of loess tunnel, the stability of surrounding rock and so on. The15#tunnel in Yintao project is a more loess-covered tunnel, whose underground water level is very shallow as well as the loess is in saturated state. Survey finds that there are serious deformation and distortion of surrounding rock in the process of tunnel excavation, such as, blocks falling, masonry lined with cracking, roof fall, collapse, etc. All the above affected the construction progress and property safety.Based on the engineering geological material over the past decades and scientific research achievements, this survey adopts the following methods; site survey, field surrounding rock deformation observation and water level monitoring and it also shows a systematic study on the deformation and distortion of surrounding rock in the15#tunnel. Considering engineering problems in the corresponding engineering management measures, the research results services Yintao project directly and led to optimize the design provides direct geological support, and also for the similar projects for reference. The research contents and results are as follows:(1) The geological environment of regional engineering is characterized as, the project is located in the fold and fracture of the composite sedimentary basin area, groundwater development is rich and water level is shallow and formation is mainly the pleistocene epoch in Q2saturated loess, the earth’s crust uplift and fault activities frequent, seismic activity for distribution plexiform features, and not even.(2) By the laboratory soil experiment to get: saturation of the physical and mechanical properties of Q2loess; the uniaxial compressive strength and slip resistance of different water content; quantitative analysis the relationship of the moisture content and loess samples compressive and shear strength.(3) After analyzing the interior of uniaxial compression creep test, the researcher showed the rheological damage of saturated Q2loess can be divided into three parts: saturated Q2loess rheological damage is divided into three stages:the initial creep stage, The isokinetic creep stage and acceleration creep stage creep stage until the damage. Uniaxial compressive load creep damage form is shear crack damage.(4) Passing the field convergence deformation monitoring test, together with the creep test research for rock deformation mechanism, saturated Q2loess compressive, and shear strength is low, after excavation of the surrounding rock stress redistribution to produce plastic deformation, creep phenomenon is obvious. Q2saturated loess tunnel stability can through the deformation velocity, acceleration and eventually convergence values to judgment.(5) For the properties of Q2loess engineering are different from those of Q3、 Q4loess, and is located Under the water level, The measures for prevention and control should be conducted as follows, set in the tunnel around the pumping wells to low groundwater levels, and then puts forward corresponding prevention and control measures, mainly for the timely drainage, strengthen the support and attention to the site monitoring, and the research results for engineering design and construction method provided the basis and the service.